Then witch hunter can be its own discussion. It isn't covered by any spec or HT. It has nothing to do with Dark Rangers. Why are you obsessed with wanting Dark Rangers be a type of Witch Hunter?
And see, this is where your reasoning breaks down. Mountain Kings and Farseers are as much 'part of other classes' as any Hero concept is 'part of other classes'. Blademaster is just a type of Warrior too, one that happens to go invis and use illusions. Warlocks are just a type of mage, one that summons demons. Even Paladin is just a type of Priest, one that melees. The definition of a WoW class is quite nebulous and free form.. Like what is an Evoker if not just a fancy name for Dracthyr Mages that lean on their bloodline powers? Lorewise, they are just a type of mage!
I think it is good that we have different identities for different types of Warriors, Mages, Wisemen/healers and Ranged Specialists. But the line between class and spec identities is not distinct in the lore. Gameplay merely adapts as it pleases, making no care if Brewmaster is just a Spec, while Evoker is a full class.
So question to you, are you more concerned about the lore or the gameplay? It seems you only want something to be a class just because it has a more prominent identity, but not really caring if a Dark Ranger becomes something else like a Witch Hunter in the process. So it doesn't seem like you care about Dark Rangers identity as much as you care about it fitting into categories that you feel most comfortable with. Like OCD > Lore.